One area of animal management that is often overlooked is how to introduce replacement animals into the herd without disturbing the “status quo” of the existing population. We had assumed these young animals would make the transition into the sow herd without any challenges and adapt quickly. To the contrary, we now understand that gilt introduction plays a vital role in overall herd stability.

A sound acclimatization program should allow a period for vaccinating young breeding stock and exposing them to farm-specific pathogens before the replacements enter the same air space as the existing sow herd. This is sometimes confused with the quarantine period of newly arrived animals. Whether you are raising your own replacements or purchasing them, an acclimatization program is useful for maintaining sound herd health.

Animals are either placed in an “off-site” facility away from the main sow unit or “on-site” buildings separated from the main barns by a hallway of some kind. On-site buildings usually are closed off from day-to-day traffic until the group has been cleared for the barn staff to take care of daily chores. Required blood or oral fluids testing is usually completed before the barn staff freely moves back and forth to the on-site facility. Most of the off-site locations have another caretaker looking after the quarantined animals.

Program for acclimation

The program for acclimatizing the new breeding stock is built on a schedule that provides vaccinations, natural exposure and a cool-down period before entering the main facility. Vaccination programs are designed to protect the replacement animals against disease pressure from the sow unit, but also provide stability to those replacements so that they do not disturb the health of the existing sow herd. There are some pathogens that we try to immunize the new breeding stock by using natural exposure. This may include fecal material from the sow herd, piglet manure from scouring litters, ropes that have been soaked in material from the sow barn or possibly live animals identified to be culled from the herd.

Once animals are immunized, a couple of weeks usually are allowed for the group to quiet down and develop antibody protection toward the diseases of concern. When replacement animals are sourced from the same farm, they usually will have a smoother transition into the herd, as they have already been exposed to many of the farm’s resident bacteria or viruses.

However, with purchased breeding stock, the movement into the sow herd could cause some flare-ups of clinical problems due to incompatibilities between the two sources. Many farms will purchase breeding stock at a younger age to allow more time for acclimatization.

When farms overlook a proper acclimatization of new gilts or boars, it may result in a potential disease risk to the sow herd or replacements. In addition, it also affects the downstream pig flow health. Pigs born during a period of unstable herd health will have disease challenges or weakened protection against the pathogens circulating in the destabilized sow herd.

At this point in the production system, the economic and performance losses begin to mount up. Therefore, consider how you can develop a solid acclimatization program for replacement breeding stock for minimizing health challenges on your farm.

Case study 1

A 600-sow unit called me out to check some finisher pigs that were looking “unthrifty” starting around 12 weeks of age. This sow unit and nursery are located on the same site, and finisher barns are on three other sites 5 to 12 miles away. The sow herd is negative for porcine reproductive and respiratory syndrome virus and positive for Mycoplasma hyopneumoniae.

The first barn I walked through had 1,200 head of the youngest finisher pigs recently moved from the nursery. There was a minimal amount of mortality, but the oldest group had 5% of the pigs that were starting to appear thin, gaunt with long hair and less active.

The barn next door, also a 1,200-head building, had the next four age groups in it. That barn had several pigs that were observed to be falling out from the groups. The pigs in question were pale, gaunt, thin and unthrifty in appearance. We chose to euthanize four of those pigs, one in each age group, and submitted tissues to the lab for diagnostic testing.

The lab results indicated a positive test for PCV2 (circovirus), with a Strep suis bacteria isolated also. I asked the owner and herd manager if the pigs were vaccinated for circovirus. They replied that every pig is picked up at weaning and injected with a one-dose PCV2 product. I became concerned that we were facing a compliance issue with vaccinations, or that the sow farm was circulating PCV2 virus.

The following week, I collected serum from sows and presuckling piglets to test for PCV2 virus. Results indicated that one sow’s serum pooling was positive, and all four piglets’ serum poolings were positive for PCV2 virus. This indicated the sow farm had become unstable for PCV2.

Upon further investigation, I learned that the farm was not vaccinating the replacement gilts for PCV2. The owner thought the purchased gilts had lifetime immunity as a result of getting PCV2 vaccine at weaning.

We discussed the importance of giving a booster injection of PCV2 vaccine to replacement females when they arrive to the farm’s isolation-quarantine facility. The farm has modified the gilt vaccination protocols to now include a PCV2 booster.

Case study 2

This farm has 2,500 sows at a breed-to-wean site and is contracted to sell all of the weaning-age pigs to one customer. The sow farm is PRRS negative and M. Hyo positive. Production is very good in the sow unit, and the weaner pig customer brags about the quality of the pigs.

I was asked by the herd manager to do a walk-through visit of the farm. She was concerned with the amount of coughing heard in the gestation barn. During the herd visit, I observed that over half of the recently bred gilts were coughing. The sows appeared to be fine. I noticed the ear tag color on the gilts was different.

The manager told me that the owner wanted to change source herds for his gilt supply because the farm could save on trucking costs for delivery. We discussed the age of the gilts at delivery and health status of the gilts. “Were they similar to the past source?” The manager answered that actually they might be better because they were M. Hyo negative. This comment sparked my attention, and I asked if the farm was handling the new source any differently than the previous one. She responded that since they were M. Hyo negative, they chose to drop the mycoplasma vaccine.

We blood-tested and nasal-swabbed 20 sows and gilts at this visit and sent the samples to the diagnostic lab. The serum samples were negative for PRRS, and nasal swabs were negative for flu, but the M. Hyo serum tests had very high titers on the gilts sampled. The sows had mixed results. This indicated gilts were likely picking up exposure to M. Hyo after entering the sow barn, thus developing the persistent cough.

I scheduled a meeting with the owner and herd manager to convey my plan for a better control plan of the mycoplasma on the new gilt source. Part of this plan included purchasing the gilts at a younger age to allow for a longer acclimatization period and intensifying the mycoplasma vaccination program. The owner agreed to the changes.

Acclimatizing your replacement stock to your sow herd is an important step toward maintaining a healthy herd. Young animals are often naïve or unprotected to pathogens circulating in a herd, especially if they are from a different source. Knowing the current health status of your existing herd and trying to match health status of an incoming source may be difficult. Discussing this important step in herd health with your veterinarian will pay dividends. With knowledge and understanding of how diseases spread, he or she can design a program that is best-suited for your herd.